Humans and Chimps had Intercourse for millions of years before a final separation

I landing on this page while reading about chimpanzee to make my daughter understand different primates. This article talks about similarities between different chromosomes of Humans and Chimps. Interestingly the autosome chromosomes separated 6-5 millions years ago but X chromosome only 2-1 million years ago. Theory says that Hybrids were interbreeding for long time before the final separation into Pan and Homo, about for 4 million years. Just think of how many interesting hybrids would have been created in this era. Leaving that why can not we find one now or a fossil ?